There's really only one step. Follow the link, and save a copy to your drive.
From there you can use all or some of the pages to track every collectible in the game.
I still need to add some photos for some of the pages (like the merlin trials) but will update here when that's done so you can copy it to your own saved checklist.

Hogwarts Legacy Completion Checklist[docs.google.com]

If you like this, think about buying me a coffee ;) @robinlygameguides